[PATCH v1 1/6] fs/readdir: Fix filldir() and filldir64() use of user_access_begin()

[Christophe Leroy]

Some architectures grand full access to userspace regardless of the
address/len passed to user_access_begin(), but other architectures
only grand access to the requested area.

For exemple, on 32 bits powerpc (book3s/32), access is granted by
segments of 256 Mbytes.

Modify filldir() and filldir64() to request the real area they need
to get access to.

Fixes: 9f79b78ef744 ("Convert filldir[64]() from __put_user() to unsafe_put_user()")
Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
---
 fs/readdir.c | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/fs/readdir.c b/fs/readdir.c
index d26d5ea4de7b..ef04e5e76c59 100644
--- a/fs/readdir.c
+++ b/fs/readdir.c
@@ -236,15 +236,11 @@ static int filldir(struct dir_context *ctx, const char *name, int namlen,
 	if (dirent && signal_pending(current))
 		return -EINTR;
 
-	/*
-	 * Note! This range-checks 'previous' (which may be NULL).
-	 * The real range was checked in getdents
-	 */
-	if (!user_access_begin(dirent, sizeof(*dirent)))
+	if (dirent && unlikely(put_user(offset, &dirent->d_off)))
 		goto efault;
-	if (dirent)
-		unsafe_put_user(offset, &dirent->d_off, efault_end);
 	dirent = buf->current_dir;
+	if (!user_access_begin(dirent, reclen))
+		goto efault;
 	unsafe_put_user(d_ino, &dirent->d_ino, efault_end);
 	unsafe_put_user(reclen, &dirent->d_reclen, efault_end);
 	unsafe_put_user(d_type, (char __user *) dirent + reclen - 1, efault_end);
@@ -323,15 +319,11 @@ static int filldir64(struct dir_context *ctx, const char *name, int namlen,
 	if (dirent && signal_pending(current))
 		return -EINTR;
 
-	/*
-	 * Note! This range-checks 'previous' (which may be NULL).
-	 * The real range was checked in getdents
-	 */
-	if (!user_access_begin(dirent, sizeof(*dirent)))
+	if (dirent && unlikely(put_user(offset, &dirent->d_off)))
 		goto efault;
-	if (dirent)
-		unsafe_put_user(offset, &dirent->d_off, efault_end);
 	dirent = buf->current_dir;
+	if (!user_access_begin(dirent, reclen))
+		goto efault;
 	unsafe_put_user(ino, &dirent->d_ino, efault_end);
 	unsafe_put_user(reclen, &dirent->d_reclen, efault_end);
 	unsafe_put_user(d_type, &dirent->d_type, efault_end);
-- 
2.25.0